20 In. As a Conductor and Surface Casing Set at 1,050m MD from a Fixed Production Platform in 33 m Water Depth, HPHT Offshore Development Wells, Successful Case History in Mexico

Abstract In offshore drilling around the world, 36 in. or 30 in. casing is commonly used as the Conductor Casing and subsequently 22 in., 20 in., or 16 in. used as the surface casing. Since the 1990s offshore Mexico, 20 in. casing has been utilized as the Conductor casing, set at a depth of 100-150 m MD below the mudline, followed by a Surface Casing string of 16 in.,13 5/8 in. or 13 3/8 in., set at approximately ~950 m below mudline. Historically, some shallow water production structures drove the 30 in. Conductor Casing in place, using a hydraulic or diesel driven hammer device. In some cases, these conductor strings only reached a few meters below the seabed due to soil strength or hammer capacity limitations. This shallow depth of conductor and associated low fracture gradient often resulted in losses while drilling the next hole section to between 500m – 1,100m below to mudline. The innovative idea surfaced to use the 20 in. as a combined Conductor and Surface Casing string, set at approximately ~950 m MD below the mudline and eliminate completely the use of 30 in. as the Conductor Casing string. This paper discusses the viability of using the 20 in. as Conductor/Surface Casing, by considering the life cycle of production loads, metocean forces on the Conductor for evaluating the strength and stability of the 20 in. casing and connections. Additionally, an anti-corrosive coating is applied on the 20 in. casing in the splash zone. Furthermore, the paper will discuss the operational aspects of drilling, running and cementing the 20 in. Casing, along with installation of the wellhead, base plate, and conductor guide shim installation, that were necessary to construct the well. The results of changing the well design by eliminating the 30 in. Conductor and utilizing the 20 in. as a combined Conductor/Surface Casing string, resulted in savings of approximately 16 days and US$6.0 MM per well, when compared to offset wells on the same facility with 30 in. Conductor installed.